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新研究揭黄河高效运送沉积物原因,有助于防洪

更新时间:2017-6-5 18:40:07 来源:纽约时报中文网 作者:佚名

A New Formula to Help Tame China’s Yellow River
新研究揭黄河高效运送沉积物原因,有助于防洪

Each year thousands of tourists flock to a reservoir along the Yellow River in China to witness a ritual cleansing so violent that it can look as if the earth just exploded. At the end of June and the start of July, for as long as two weeks before the flood season, Chinese officials open large portals along the walls of the Xiaolangdi Dam, releasing clear and muddy water simultaneously from the reservoir above to the river below. It gushes out, and in some years clouds the color of doom ascend beyond the dam’s walls.

每年,成千上万的游客蜂拥来到中国黄河边的一个水库,观看一场例行的泄洪,整个过程非常激烈,状似山崩地裂。在六月底、七月初汛期前的两周里,中国官方会打开小浪底大坝的巨大闸门,同时从上方的水库中放出清水和浊水,流入下方的河中。水喷涌而出,在有些年份,大坝上方显现出末日的颜色。

The Yellow River is considered the cradle of China’s civilization — but also its sorrow. Its vast floodplains coaxed people in for agriculture. Yet its violent floods have killed millions.

黄河被认为是中华文明的摇篮,但也是苦难之源。它广阔的泛滥平原吸引人们来这里从事农业。但它凶猛的洪水也导致了成百上千万人丧生。

The precautionary purging at the Xiaolangdi Dam, which has occurred annually since 2002, is the latest high-tech attempt to prevent flooding and tame the Yellow River, which today threatens more than 80 million people. It carries sediment more concentrated than in any other river in the world — so much that tiny particles of sand and silt clog reservoirs, raise riverbeds, break levees and cause potentially catastrophic floods. During what is called the Water and Sediment Regulation Discharge Project at Xiaolangdi Dam, muddy water evacuates sediment from the reservoir, and clear water washes sand out from the channel below to reduce flood risk.

小浪底大坝的预防性泄洪从2002年起每年进行一次,是预防洪水、制服黄河的最新高科技尝试。如今,黄河威胁着8000多万人的生命。它携带的沉积物含量超过世界上任何一条河流,微小的沙砾和淤泥阻塞水库,抬高河床,冲破堤坝,可能导致灾难性洪水。在小浪底的调水调沙工作中,浊水将水库中的沉积物排出,清水把下方渠道中的沙子冲走,以减少发生洪水的风险。

The annual purge can lower the riverbed by about six feet a year on average, but a surprising discovery about the river’s bottom, as well as its unusual capacity to carry high loads of sediment, could one day mean that the purge may not be as effective at preventing floods. In a study published last month in the journal Science Advances, researchers suggest new considerations to take into account when conducting this yearly event.

泄洪能把河床平均每年降低约六英尺,但是一项关于河底的意外发现,以及黄河运送大量沉积物的不寻常能力,可能意味着将来有一天,这种泄洪方式在防洪方面不会产生同样的效果。在上个月《科学前沿》(Science Advances)杂志发表的一项研究中,研究人员建议在今年的泄洪工作中,将一些新的因素考虑在内。

Previous models couldn’t explain how the Yellow River transports about a billion tons of sediment thousands of miles to the sea each year. Compared with the Mississippi River, it holds three times as much sediment and just a tenth of the water. But Hongbo Ma and Jeffrey A. Nittrouer, both geologists at Rice University and lead authors of the study, examined historical data and scanned the bed of the river with 3-D sonar.

之前的模型不能解释黄河如何每年携带约10亿吨沉积物,奔流数千英里,运到海里。黄河运送的沉积物量是密西西比河的三倍,而运送的水量仅为它的十分之一。不过,赖斯大学(Rice University)的地质学家、这项研究的主要作者马宏博和杰弗里·A·尼特劳尔(Jeffrey A. Nittrouer)研究了历史数据,用3D声纳设备扫描了黄河河床。

“It was very striking to see that the Yellow River bottom is basically flat,” Dr. Ma said.

“我们非常意外地看到,黄河的河底基本上是平的,”马宏博说。

It was assumed that the river’s flow produced relatively tall, closely spaced dunes that slowed the water and sucked up energy that might otherwise be available for sediment transport. But the Yellow River, with its fine sediment particles, had low dunes spaced far apart, freeing more energy to move the sediment.

人们曾经认为,河水的流动会产生相对较高、密集排列的沙丘,它们会降低水速,减少本来可用于运送沉积物的动能。但是,黄河沉积物的颗粒很小,所产生的沙丘较低,而且相距较远,所以保留了更多推动沉积物的动能。

With this discovery, the researchers and their colleagues developed a universal formula that could be used on all kinds of rivers to predict the exact sediment amounts traveling in the fluid. They can better predict where and when floods will occur or new land will be formed.

这两位研究者和同事们根据这项发现得出了一个通用公式,用于精确推算各种河流在流动中运送的沉积物量。他们可以更好地预测洪水或新的土地会于何时在哪里形成。

“We want to make the Yellow River the poster child of rivers and deltas around the world,” Dr. Nittrouer said.

“我们想把黄河变成世界各地河流和三角洲的典型代表,”尼特劳尔说。

At the Xiaolangdi Dam, competing systems may simultaneously lower the riverbed as clear water flushes away sediment and raise it as sandy water forms dunes that slow the sediment flow. Combining the new formula with the old model could help operators prevent more floods by achieving a better balance between the systems.

在小浪底大坝,相互冲突的系统可能同时降低和抬高河床,前者是因为清水能冲走沉积物,后者是因为含有沙子的河水会形成沙丘,减缓沉积物的流动。新公式和旧模型的结合可以帮助管理者在这些系统之间实现更好的平衡,从而预防洪水。

Last year, officials unexpectedly canceled the release because there wasn’t enough water or muck to need flushing, possibly because of lighter rainfall.

去年,官方出人意料地取消了泄洪,因为当年没有足够的水或淤泥需要冲刷,可能是因为降雨量较少。

To not disappoint tourists, they released clear water from the dam for just 15 minutes.

为了不让游客失望,他们仅从坝上放了约15分钟清水。

It’s unclear what to expect this year. “It would have to be the end of June or July,” Dr. Ma said, “but honestly we’re not aware of whether this event will happen or not.”

尚不清楚今年会是什么情况。“要等到六月底或七月才知道,”马宏博说,“不过坦白地讲,我们并不确定这项工作是否会进行。”

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